1. Field of the Invention
The present invention relates to a coating for components which are exposed to high temperatures and aggressive media, e.g. components of gas turbines and in particular aircraft engines. In addition, the present invention relates to a process for producing such coatings and also components produced in this way.
2. Discussion of Background Information
The addition of chromium and/or aluminum as alloying constituents to alloys in order to effect corrosion and/or oxidation protection in the high-temperature range for the materials alloyed therewith is known from the prior art. The addition of chromium and/or aluminum results in formation of frequently slow-growing chromium oxide or aluminum oxide layers under corrosive and oxidizing conditions of this type, and these oxide layers can protect the material against further attack. Depending on the composition of the material to be protected and the specific use conditions, either chromium or chromium-rich layers or aluminum or aluminum-rich layers are employed.
In addition, the formation of corrosion protection layers and/or high-temperature oxidation protection layers which can likewise contain chromium and/or aluminum is also known in many different applications.
Furthermore, it should be noted that such protective layers also have to have mechanical properties which avoid damage or destruction of the protective layers under the given use conditions, since mechanical damage to the layers can once again lead to increased corrosive attack or oxidative attack. Accordingly, many coatings having proportions of chromium and/or aluminum are known in the prior art. An example is given in WO 2006/026456, the entire disclose of which is incorporated by reference herein, in which chromium layers which have a chromium content of 30% and additionally comprise aluminum are described. A further example is described in DE 10 2008 039 969 A1, the entire disclose of which is incorporated by reference herein, which discloses chromium layers having a chromium content of more than 30% by weight.
In the case of gas turbines and in particular aircraft engines, components which are operated in environments at which both high temperatures and also aggressive media occur are used. Thus, aircraft are operated, for example, above the sea or close to the sea and salt-containing air and accordingly also salt particles can therefore be introduced into the engines. In addition, further elements such as sulfur, sodium, calcium and potassium which can bring about corrosion can be present due to the fuel. Since the engines also have high operating temperatures during operation, severe high-temperature oxidative conditions also prevail. As a consequence, components of this type, for example turbine blades in the low-pressure turbine of an aircraft engine, have to withstand high temperatures and also be protected against corrosion, e.g. sulfidation. However, the coatings known hitherto do not give a satisfactory result here.
It is therefore desirable to have available a coating which protects against high-temperature oxidation and corrosion for components which are exposed to high temperatures and corrosion, in particular components of gas turbines and aircraft engines. In addition, a process for corresponding coating of components, which is simple to carry out and allows reliable coating and offers high-temperature oxidation protection and corrosion protection to components subject to such stress is desirable. It further is desirable to have available components of this type, e.g. turbine blades of aircraft engines and in particular low-pressure turbine blades.